1. Field of the Invention
This invention relates to an organic photoconductive composition comprising dicarbazolyl cyclobutane, and more particularly, to the use of dicarbazolyl cyclobutane in combination with a nitrofluorenone and their use in electrophotographic processes.
2. Description of the Prior Art
The forming and developing of images on the surfaces of certain photoconductive materials, by electrostatic means, is now well known. Carlson, in U.S. Pat. No. 2,297,691 teaches the basic xerographic process, which involves uniformly charging a photoconductive insulating layer and then exposing the layer to a light-and-shadow image which dissipates the charge on the portions of the layer which are exposed to light. The electrostatic latent image formed on the layer corresponds to the configuration of the light-and-shadow image. In another modification, a latent electrostatic image is formed on the photoconductive insulating layer by charging the layer in image configuration. A finely divided developing material comprising a colorant called a toner and a toner carrier is deposited on the image layer. The developing material is normally attracted to those portions of the layer which retain a charge, thereby forming a powder image corresponding to the latent electrostatic image. The powder image may then be transferred to paper or any other receiving surface. The powder image is permanently bonded to the paper by any suitable fixing means. Typically, a heating process, called fusing, is used, as described in U.S. Patents such as, U.S. Pat. Nos. 2,357,809, 2,891,011 and 3,079,342.
It is possible to employ a wide variety of photoconductive insulating materials in the electrostatic process. For example, Carlson, in U.S. Pat. No. 2,297,691 discloses photoconductive insulating materials such as anthracene, sulfur, selenium or mixtures thereof.
These materials generally have sensitivity in the blue or near ultraviolet range, and all but selenium have a further limitation of being only slightly light sensitive. For this reason, selenium has been the most commercially accepted material for use in electrophotographic plates. Vitreous selenium, however, while desirable in most aspects, suffers from serious limitations in that its spectral response is somewhat limited to the ultra-violet, blue and green region of the spectrum, and the preparation of vitreous selenium plates requires costly and complex procedures, such as vacuum evaporation. Also, selenium plates require the use of a separate conductive substrate layer, preferably with an additional barrier layer deposited thereon before deposition of the selenium photoconductor. Because of these economic and commercial considerations, there have been many recent efforts towards developing photoconductive insulating materials other than selenium for use in electrophotographic plates.
It has been proposed that various two-component materials be used in photoconductive insulating layers used in electrophotographic plates. For example, the use of inorganic photoconductive pigment dispersed in suitable binder materials to form photoconductive insulating layers is known. It has further been demonstrated that organic photoconductive insulating dyes and a wide variety of polycyclic compounds may be used together with suitable resin materials to form photoconductive insulating layers useful in binder-type plates. In each of these two systems, it is necessary that at least one original component used to prepare the photoconductive insulating layer be, itself, a photoconductive insulating material.
In a third type plate, inherently photoconductive polymers are used; frequently in combination with sensitizing dyes or Lewis acids to form photoconductive insulating layers. Again, in these plates at least one photoconductive insulating component is necessary in the formation of the layer. While the concept of sensitizing photoconductors is itself commercially useful, it does have the drawback of being limited to only those materials already having substantial photoconductivity.
The above discussed three types of known plates are further described in U.S. Pat. Nos. 3,097,095; 3,113,022; 3,041,165; 3,126,281; 3,073,861; 3,072,479; 2,999,750; Canadian Pat. No. 644,167 and German Pat. No. 1,068,115.
The polymeric and binder-type organic photoconductor plates of the prior art generally have the inherent disadvantages of high cost of manufacture, brittleness, and poor adhesion to supporting substrates. A number of these photoconductive insulating layers have low temperature distortion properties which make them undesirable in an automatic electrophotographic apparatus which often includes powerful lamps and thermal fusing devices which tend to heat the xerographic plate. Also, the choice of physical properties has been limited by the necessity of using only inherently photoconductive materials.
Inorganic pigment-binder plates are limited in usefulness because they are often opaque and are thus limited to use in systems where light transmission is not required. Inorganic pigment-binder plates have the further disadvantage of being nonreusable due to high fatigue and rough surfaces which make cleaning difficult. Still another disadvantage is that the materials used have been limited to those having inherent photoconductive insulating properties.
The use of poly-N-vinylcarbazole alone, or in combination with trinitro-fluorenone, as a photoconductor is taught in the prior art, as for example, in U.S. Pat. No. 3,037,861 to Hoegl and U.S. Pat. No. 3,484,237 to Shattuck et al.
The preparation of coatings of poly-N-vinyl carbazole and trinitro-fluorenone involves dissolving the polymerized vinylcarbazole in a solvent such as tetrahydrofuran, benzene, toluene, dioxane or dichloro methane followed by the addition of 2, 4, 7-trinitro-9-fluorenone to the polymer solution and mixing the solution for about 30 minutes to more than an hour. The difficulty of dissolving the polymer tends to increase processing time and increase the complexity of the process.
The N-vinyl-carbazole monomer is very soluble in organic solvents but is a very poor photoconductor. The monomer forms an orange charge transfer complex with trinitro-fluorenone which is very insoluble even in tetrahydrofuran and is a very poor photoconductor.